Pompey have been relegated to League Two.
Oldham’s 1-0 triumph at home to Yeovil – courtesy of a Matt Smith strike – sealed the Blues’ fate.
Guy Whittingham’s side are now eight points adrift of safety with just two games remaining.
The result also means it is now likely Pompey will begin life in League Two with a 10-point deduction next term as they prepare to exit administration.
Owners-in-waiting, the Pompey Supporters’ Trust, expect the points loss to come off this season.
However, that has not been confirmed. And with the Blues already down, the pressure from other clubs to give them a sufficient punishment may mean the 10-point deduction will be carried into the start of their League Two campaign.